I use that one for filling the dragons mouth heater I have in the garage.I use this funnel for years and yes, I've also had the experience of it buckling away when the oil level in the funnel adds weight. I always use a fun construction of tension bands between the 3c and a camping chair to hold it in place. In addition to the weight from the oil which has to be taken in account, also the lower fixation is important - it must not slip out of the filling hole at the bottom.
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Well, I get along with it, at least it's orange ...